1. Field of the Invention
The present invention relates to a slip ring assembly for supplying electric signal and electric power to a rotative body incorporated in various instruments, and to the manufacturing method thereof. More particularly, the present invention relates to those in which a simplified assembly procedure, reduced defect occurrence rate and lower production cost are accomplished.
2. Description of the Related Art
There are several examples of slip ring assembly in the prior art, such as the Japanese non-examined publication (Kokai) No. Sho 55-159581, U.S. Pat. No. 3,599,165, and also U.S. Pat. No. 4,326,769.
The slip ring assembly as disclosed above typically comprises two sections of elements, that is, a fixed base unit mounted on any instrument incorporating a rotative body, and a rotor unit rotatively accommodated in the fixed base unit and electrically connected to the rotative body via a plurality of lead wires.
The fixed base unit has a plurality of brushes connected to the lead wires, and the rotor unit similarly has a conductive ring connected to the lead wires. With this structure, when the rotor unit rotates, the brushes on the side of the fixed base unit are constantly in contact with the conductive ring, thereby the electric power and the signal can be supplied to the rotative body.
The structure of the fixed base unit and the rotor unit is described below, in particular to the production method thereof. First, as for the fixed base unit, the brushes to which the lead wires are connected are placed inside the insert-injection mold into which the heat-setting resin is injected, so that the fixed base unit integrally incorporating a plurality of brushes may be obtained. In this connection, since the brushes may be distorted during insert molding, the correction of the brushes should be carried out after completion of insert molding in order to adjust the contact pressure to the conductive ring.
As for the rotor unit, the conductive ring to which the lead wires are connected is then placed inside the insert mold, and the heat-setting resin is injected into the mold. Thus the rotor unit integrally incorporating the conductive ring is obtained. Then the conductive ring is exposed by lathe working. This lathe working should be carried out since the resin has covered the surface of the conductive ring (the contact surface with the brush) when the rotor unit is molded. In addition, the gold-plating is applied thereto after the lathe working in order to obtain the stable conduction.
Then the rotor unit is placed and accommodated in the fixed base unit, then a desired slip ring assembly is obtained by adding various arrangements accompanied thereto. The slip ring assembly is then attached to any instrument, and the plurality of lead wires are connected to the rotative body of the instrument. Accordingly, when the rotative body rotates, the rotor unit also rotates in a state that the necessary electric power can be supplied to the rotative body without the plurality of lead wires being twisted, thereby the signal communication between the rotative body can be accomplished.
However, the above prior arts have the following disadvantages.
First, since the rotor unit has been produced by insert molding, when there is a conduction defect in regard to any one of the plurality of the conductive parts (i.e. conductive ring), the whole unit of the rotor should be replaced. This means the overall abandonment of the rotor unit in spite of existence of the minimum part of the defective conduction, which might lead to the rise in maintenance cost. This problem becomes more serious when the number of the conductive rings increases.
This may also be applied to the case of the fixed base unit. That is, when there is a conduction defect in regard to any one of the plurality of the conductive parts (i.e. brushes), the whole body of the fixed base unit should be abandoned and replaced to a new, whole fixed base unit.
Further, in regard to the gold-plating for the rotor unit, such a gold-plating should be carried out after completion of the insert molding as well as the lathe working (that is, in a complete state as a rotor unit). According to the ordinary method of plating, the object to be plated should be soaked in the plating bath, and in this case, since the whole rotor unit must be soaked, any other parts not subject to be plated (i.e. parts except the conductive rings) should also be soaked in the plating bath. Consequently, the number possible to be plated at one time is seriously reduced, which might result in the increase of the plating cost.
In addition, as above discussed, since the brushes may be distorted due to molding pressure of the insert molding, the form of the brushes should be corrected after completion of the molding, which might also result in the increase of the production cost.
It also should be noted that, since the rotor unit and the fixed base unit should be produced by insert molding, it is necessary to use any material having strong coating effect against high temperature (e.g. "Teflon" coated material) for the lead wires, connected to the conductive ring and the brushes, by soldering (welding). Consequently, the higher manufacturing cost should be incurred.
It should also be noted that, each time when the slip ring assembly having a different number of electrodes is produced, it is necessary to prepare the specialized inserting molds used only for such a rotor unit as well as for such a fixed base unit. Accordingly, it is impossible to prepare a common mold which can be used for various types of slip ring assembly having different number of electrodes, thus the cost therefor becomes considerably high.